ST9401WA-CS 950329WIER & ASSOCIATES, INC.
March 29, 1995
Mr. Kenneth Griffin, P.E.
City Engineer
Engineering Department
City of Coppell
255 Parkway Boulevard
Post Office Box 478
Coppell, TX 75019
214~462-0022
RE: W&A # - 94093, DENTON TAP ROAD;
Coppell, Texas
Dear Ken:
We met on March 20th with yourself, Mike Martin, Rick Wieland and Michael
Carr regarding criteria for providing for a continuous high speed bicycle path system
along Denton Creek to the proposed Denton Tap Road design. The bike path concept
discussed consisted of a high speed path along the south side of Denton Creek from
the west up to Denton Tap Road then crossing over the proposed bridge to the north
and proceeding to the east along the north side of Denton Creek. The original cost
studies we performed at the contract phase included pedestrian crossings over the
bridge and a ten foot wide path under the bridge on both sides of the creek. You asked
that we prepare a preliminary bike path plan layout which demonstrates a bike path
plan, bridge layout, pavement lanes, pedestrian walkways, hike and bike trail, and
pedestrian crossing locations. You also asked us to determine the additional cost over
our original cost opinion to allow for future addition of a high speed bike path crossing
under and over the proposed roadway bridge at Denton Creek.
The plan, costs, and comments are discussed below. In the discussion that
follows, the existing parks south of Denton Creek are referred to as Brown east and
Brown west. The future park north of Denton Creek and west of the roadway is referred
to as future Magnolia Park. The private property located north of the creek and east of
Denton Creek is referred to as the Vista Ridge tract. The comments we make in the
following are not intended to encourage or discourage addition of bike trail facilities, but
are intended to provide cost, impact, and visual aids to assist the city in the decision
process:
Mr. Ken Griffin, P.E.
W&A #94-093
March 29, 1995
Page 2 of 5
PLAN INDICATING PHYSICAL CONDITIONS
We reviewed the existing topography, vegetation, park locations, and other
physical conditions to arrive at a layout for the bicycle and walkway locations
indicated on the attached preliminary plan. The plan indicates a continuous high
speed bike path along the south side of Denton Creek crossing under the
proposed bridge then curving within Brown East Park terminating at a stop
location at the future park entrance at Denton Tap Road. The bike path then
traverses north along the east side of Denton Tap Road over the future bridge to
the north side of Denton Creek. The bike path then curves away from the
roadway and traverses to the east along the north side of Denton Creek. The
trail system shown on the plan and exhibits meets the recommended AASHTO
design criteria as follows:
B.
C.
D.
E.
F.
G.
12' typical paved width with 2' flat clear space.
16' paved width at bridge overpass and under bridge.
Maximum 5% vertical grade.
Minimum 155' horiz. curve radii.
10' vertical clearance beneath bridge.
10' safety barrier over bridge.
Separated from pedestrian paths (non multi-use path).
The above criteria is recommended but can be reduced if situations and
restraints dictate lesser design criteria. The plan also indicates the location of
pedestrian walkways which are separated from the bicycle path. Also attached
are typical sections indicating the path system at the bridge and at the roadway
embankment. The sections and plans do not attempt to indicate landscaping
and other ascetic features.
Several items we would wish to bring to your attention regarding the attached
plan are discussed below:
Path Impacts on Parks: The alignment as indicated will substantially
impact the layout of Brown Park East. The alignment could be altered by
stop and turns to illuminate Iooping well into the park. The existing creek
bank is steep on each side and the path elevation at 10' below the bridge
low cord will be in an approximately 8' deep cut exiting the bridge. The
maximum 5% vertical grade on the path and 155 horizontal curve radii will
cause the cut into the bank to extend into treed bank for about 90'
upstream and downstream of the bridge. This will require substantial
removal of trees along the creek bank on the west side of the bridge.
Also expensive retaining walls and barrier fence will be required on the
outside creek side of the path. The path system outside of the bridge
Mr. Ken Griffin, P.E.
W&A #94-093
March 29, 1995
Page 3 of 5
location will not be a part of the Roadway Construction and we
understand the city will attempt to fund this work by an ISTEA grant. The
creek is erosive and unstable where trees are removed and the retaining
wall foundation along the outside creek side of the path will probably
need to be supported by piers for some of the length.
Path Impacts on Private Property: The path system if crossed to the north
side of Denton Creek will traverse along the Vista Ridge tract. The path
will need to be in the overbank area which is above the 100 year flood
plain. The right-of-way will therefore be within useable property which we
anticipate will be acquired by purchase. The path right-of-way may be
quite expensive to purchase in this location. Consideration may be given
to keeping the bike path along the south side of Denton Creek to another
crossing location further to the east. A bridge crossing will ultimately be
needed, however the right-of-way costs may be substantially less for an
alternate alignment.
o
Pedestrian Walkways: The attached plans and sections indicate a 5' to 6'
walkway in all locations except the bridge crossing on the west side of
Denton Tap Road. Since this path will connect pedestrian and slow bike
traffic between two parks, we recommend the crossing over the bridge be
widened to 10' for increased safety. As indicated before, pedestrian
traffic is separated from the high speed bike path. if a under bridge
crossing is required from Brown Park East and Brown Park West, a
separate path approximately 5' wide would be recommended with a
barrier between. This would increase the total bridge length another 6'.
Our original anticipated bridge span length was 160'. Adding one bike
trail would increase the length to 166' and adding one bike trail and a
pedestrian path would increase the length to 172'.
II. ADDITIONAL COSTS
The path systems extended beyond the underpass beneath the bridge and the
overpass at the bridge are not included in the costs provided. Costs for the
path, retaining walls beyond the bridge, excavation, and widened roadway
embankment are not included. You had asked us if there was a way to design
the bridge so the path could be added to the side of the bridge in the future as a
cantilevered situation. We looked at this option and a method can be
accomplished by adding a triangular thickened section to the outside edge of the
outside column and internal cross members between columns. This option
would look gaudy and another method with similar costs can be accomplished.
We would suggest installing two additional columns with the main bridge
construction and widening the interior bridge bents as shown on the attached
Mr. Ken Griffin, P.E.
W&A #94-093
March 29, 1995
Page 4 of 5
bridge section. The "1" beams, deck, and barrier for the bike path could be
added in the future. Our cost estimates are provided below which include a
phased path crossing at the bridge and the cost to install the bike path with the
roadway bridge.
Option "A'" provide for path crossing over bridge in future:
1. Extend bridge length 6' for bike path .....................$23,000
2. Barrier rail vs pedestrian trail .................................2,400
3. Wider trail beneath bridge .....................................1,600
4. Extra piers and bent for future trail ........................18,200
$45,200
Option "B" provide path crossing with roadway bridge in current
construction:
2.
3.
4.
Extend bridge length 6' for bike path .....................$23,000
Barrier rail vs pedestrian trail .................................2,400
Wider trail beneath bridge .....................................1,600
Widen bridge 17' for bike path .............................93,600
$120,600
The above costs exclude extending the bridge length an additional 6' in
length to allow for a pedestrian walkway along the edge of the bike path
which would cost an additional $23,000. Also, the above costs do not
include widening the roadway embankment for the bike path for either
option. The embankment widening will require import of offsite material
which we estimate will cost approximately $8.00 per cubic yard. We
estimate the additional embankment to cost $20,500. This cost can be
delayed however the slope should not be landscaped in this area since it
would be removed in the future to add the embankment.
Mr. Ken Griffin, P.E.
W&A #94-093
March 29, 1995
Page 5 of 5
Ken we hope this information will help the city make decisions regarding bike
path location and design. Please contact us if you have any comments or questions
regarding this letter report.
Very truly yours,
NE III, P.E., R.P.LS.
Executive Vice President
WIER & ASSOCIATES, INC.
UTL:ckw
CC:
Rick Wieland
Mike Martin